Field of the Invention
The present invention relates to a displacement detecting device used when performing positioning and detecting an amount of displacement in the linear direction in a machine tool, an industrial machine, a robot, etc., and to a scale used in the displacement detecting device.
Description of the Related Art
Conventionally, a scale and a displacement detecting device including a detection head are used to detect an amount of linear movement and a linear position for positioning, controlling, position displaying, etc., of a machine tool, an industrial machine, a robot, etc. Further, in recent years, a displacement detecting device is also proposed, which detects an absolute position of a detection head with respect to a scale by detecting an origin mark using a vernier scale, not only an amount of displacement (movement) of the detection head.
As a conventional displacement detecting device of this type, for example, there is one as described in Patent Literature 1. The displacement detecting device described in Patent Literature 1 includes a scale in which a first region in which position information is recorded at predetermined intervals and a second region in which position information is recorded at intervals different from those in the first region are formed. Further, the displacement detecting device described in Patent Literature 1 includes a first reading unit configured to read position information in the first region and a second reading unit configured to read position information in the second region.
Then, in the displacement detecting device described in Patent Literature 1, when a difference between a first phase detected by reading position information in the first region and a second phase detected by reading position information in the second region becomes an arbitrarily set value, an origin signal is generated. By taking the origin signal to be a reference, the absolute position of the detection head with respect to the scale is detected. That is, in the displacement detecting device described in Patent Literature 1, by the phase difference between the first region and the second region, the origin mark is formed arbitrarily.
[Patent Literature 1] Japanese Patent Laid-Open No. 2004-170153